The present invention relates to a multilayer printed circuit board which can be employed as a package substrate on which electronic elements, such as integrated circuit (IC) chips, are mounted. More particularly, the present invention relates to a multi-layer printed circuit board constituted by building interlayer resin insulating layers up on a core substrate and a method of manufacturing a multi-layer printed circuit board.
Hitherto, a buildup multi-layer printed circuit board has been manufactured by a method disclosed in Japanese Patent Laid-Open No. 9-130050.
That is, an interlayer resin insulating layer is built on a core substrate having through holes formed therein. Then, a circuit pattern is formed on the interlayer resin insulating layer. The foregoing process is repeated so that the buildup multilayer printed circuit board is obtained.
At present, the through holes are formed in the core substrate by forming penetrating openings by using a drill. Therefore, the smallest limit of the diameter of the penetrating opening is 300 xcexcm. The density of the through holes cannot be raised to a value larger than a value which is defined by the diameter of the drill. Hence it follows that a method using a laser beam to form the core substrate has been investigated. Since the core substrate has a thickness of about 1 mm, fine through holes cannot, however, easily be formed.
On the other hand, the multi-layer printed circuit board, which is employed as the package substrate, must efficiently diverge heat generated in the IC chip. The multi-layer printed circuit board incorporates a core substrate which is constituted by a laminated resin board having a thickness of about 1 mm and on which an interlayer resin insulating layer having a thickness of several tens of xcexcm and a circuit layer are laminated. Therefore, the thickness of the multi-layer printed circuit board is mainly made up by the core substrate. That is, the core substrate causes the thickness of the multi-layer printed circuit board to be enlarged and the thermal conductivity to be decreased.
To solve the above-mentioned problems, an object of the present invention is to provide a multi-layer printed circuit board and a method of manufacturing a multi-layer printed circuit board capable of raising the density at which the through holes are formed and reducing the thickness thereof.
Another object of the invention is to prevent the occurrence of warpage and cracking of the upper interlayer resin insulating layer and conductor circuits.
When through holes are formed by laser beams, disconnection sometimes occurs in a heat cycle or the like. Thus, satisfactory reliability cannot be obtained. The cause of the disconnection has been investigated, resulting in detection of mixture of air bubbles in the resin with which the through hole is filled.
The cause of mixture of the air bubbles has furthermore been investigated by the inventor of the present invention. As a result, the mixture is caused by residual burrs of copper foil inwards extending from the opened portion of the through hole when the through holes are formed in a copper-clad laminated board which constitutes the core substrate. That is, as shown in FIG. 70(A), when a through hole 633 is, by a laser beam, formed in a core substrate 630 constituted by laminating copper foil 632, a burr 632b of the copper foil 632 undesirably left at the edge of the opening of the through hole 633. A tapered through hole 633 is sometimes formed. When a plated film 635 is formed to form the through hole 636 as shown in FIG. 70(B), air bubble E is sometimes left between the burr 632b and the plated film 635. When the through hole 636 is filled with a resin filler 640 as shown in FIG. 70(C), air bubble E is sometimes left between the reverse side of the portion including the burr 632b and the resin filler 640. As shown in 70(D), the portion including the burr 632b of the copper foil extending inwards sometimes prevents smooth injection. In the foregoing case, a portion which is not filled with resin filler 640 is detected in the through hole 636. Thus, a fact has been detected that the reliability in the connection of the printed circuit board deteriorates owing to the air bubble and the non-filled portion.
Since the hole forming operation using the laser beam is performed, an oxidation-reduction layer is formed as a process which is performed before the laser beam is applied and the number of laser shots is increased. Thus, the process takes a long time and the cost is enlarged.
To overcome the above-mentioned problems, the inventor of the present invention has attempted to employ a BT (Bismaleimide-Triazine) resin board as the core substrate. A fact has, however, been detected that the BT resin board having a flat surface encounters deterioration in the adhesiveness with a metal film formed on the right side of the core substrate. Therefore, the inventors or the present invention have attempted to improve the adhesiveness with the metal film formed on the right side of the core substrate by employing a resin film constituted by dispersing soluble particles in refractory resin. Thus, there arises problems in that the resin film, however, encounters decrease in the strength required for the core substrate and the interlayer resin insulating layer cannot be formed in the upper layer.
To overcome the foregoing problems, another object of the present invention is to provide a printed circuit board and a method of manufacturing a printed circuit board capable of forming adequately forming through holes by using laser beams.
Since the core substrate is filled with core materials, such as glass cloths, the laser beam must be applied to each hole for a long time to form the through holes in the core substrate having a thickness of about 1 mm by using laser beams. To form hundreds of through holes, an excessively long machining time is required and the manufacturing cost cannot be reduced. On the other hand, the through holes each having a small diameter sometimes encounters disconnection during the heat cycle. Therefore, satisfactory reliability cannot be realized as compared with conventional through holes formed by drilling and each having a large diameter.
To achieve the foregoing objects, a still further object of the present invention is to provide a multi-layer printed circuit board and a method of manufacturing a multi-layer printed circuit board capable of improving high-frequency characteristics of a ground line and a power supply line and preventing a malfunction of an IC chip caused from insufficient quantity of electric power to be supplied.
On the other hand, the diameter of each penetrating opening can be reduced as compared with an opening which is formed by drilling when the penetrating openings are formed in the core substrate by using laser beams. When the penetrating openings are formed in a copper-clad laminated board employed to serve as the core substrate, the number of laser shots are increased excessively and an excessively long time is required. When the openings are formed by the laser beams, a portion of copper for forming copper foil on the surface of the inner wall of the through hole is undesirably left. It leads to a fact that undesirable separation of the plated film formed in the through hole takes place.
To overcome the foregoing problems, its still further object of the present invention is to provide a printed circuit board excellent in connection characteristics and reliability and permitting a high-density structure which is manufactured by forming openings in a resin plate which serves as a core substrate by using laser beams and by performing sputtering to for a sputtered layer to form penetrating opening each having a small diameter and which is free from any separation of the plated films in the through holes and a method of manufacturing a printed circuit board.
To solve the above-mentioned problems, a multi-layer printed circuit board recited in claim 1 is characterized by comprising: a core substrate incorporating a metal layer sandwiched by resins; and an interlayer resin insulating layer built up on said core substrate.
A multi-layer printed circuit board recited in claim 2 is characterized by comprising: an interlayer resin insulating layer built up on a core substrate thereof, wherein
said core layer is constituted by sandwiching a metal layer between two resin layers, and a conductor is provided for each of non-penetrating openings which are formed in said resin and which reach said metal layer so that through holes are formed.
A method of manufacturing a multi-layer printed circuit board recited in claim 3 comprises at least the following steps (A) to (C):
(A) forming a resin insulating layer on an upper layer of a resin insulating layer having an upper surface on which a metal layer is formed so that a core substrate is formed;
(B) forming non-penetrating openings in said resin insulating layer of said core substrate by applying laser beams such that said non-penetrating openings reach said metal layer; and
(C) providing a conductor for each non-penetrating opening formed in said resin insulating layer so that through holes are formed.
Multi-layer printed circuit boards claimed in claims 1 and 2 and a method of manufacturing a multi-layer printed circuit board claimed in claim 3 are arranged to maintain required strength of a core substrate thereof by sandwiching a metal layer by resin. Thus, the thickness of the core substrate can be reduced. Hence it follows that the thickness of the multi-layer printed circuit board can be reduced. Since non-penetrating openings which reach the metal layer are simply required to be formed in the resin layer, the depth of each of penetrating openings which are formed by laser beams can be reduced to half or smaller as compared with the conventional core substrate. Therefore, fine non-penetrating openings can easily be formed by laser beams and, therefore, through holes each having a small diameter can be formed. As a result, a degree of integration of the multi-layer printed circuit board can be raised. Moreover, the core substrate is formed into the multilayer structure and, therefore, the metal layer between resin portions which constitute the core substrate permits wiring to be arranged. As a result, the number of layers of the multi-layer printed circuit board can be reduced. Since the non-penetrating openings are filled with plating, the intensity increases and the warpage does not easily occur.
A method of manufacturing a multi-layer printed circuit board recited in claim 4 comprises at least the following steps (A) to (D):
(A) etching a metal layer of a one-side metal-clad resin plate to form a circuit pattern;
(B) laminating a resin film to the surface of said circuit pattern to constitute a core substrate;
(C) forming non-penetrating openings in a resin insulating layer of said core substrate by applying laser beams such that said non-penetrating openings reach said circuit pattern; and
(D) providing a conductor for each non-penetrating opening of said resin insulating layer to form through holes.
A method of manufacturing a multi-layer printed circuit board recited in claim 5 comprises at least the following steps (A) to (E):
(A) etching a metal layer of a one-side metal-clad resin plate to form a circuit pattern;
(B) coating the surface of said circuit pattern with resin and polishing said circuit pattern so that said circuit pattern is flattened;
(C) laminating a resin film to the surface of said circuit pattern to constitute a core substrate;
(D) forming non-penetrating openings in a resin insulating layer of said core substrate by applying laser beams such that said non-penetrating openings reach said circuit pattern; and
(E) providing a conductor for each non-penetrating opening of said resin insulating layer to form through holes.
Methods of manufacturing a multi-layer printed circuit board claimed in claims 4 and 5 are arranged to maintain required strength of a core substrate thereof by sandwiching a circuit pattern by resin. Thus, the thickness of the core substrate can be reduced. Hence it follows that the thickness of the multi-layer printed circuit board can be reduced. Since non-penetrating openings which reach the circuit pattern are simply required to be formed in the resin layer, the depth of each of penetrating openings which are formed by laser beams can be reduced to half or smaller as compared with the conventional core substrate. Therefore, fine non-penetrating openings can easily be formed by laser beams and, therefore, through holes each having a small diameter can be formed. As a result, a degree of integration of the multi-layer printed circuit board can be raised. Moreover, the core substrate is formed into the multilayer structure and, therefore, the circuit pattern between resin portions which constitute the core substrate permits wiring to be arranged. As a result, the number of layers of the multi-layer printed circuit board can be reduced.
To solve the above-mentioned problems, a multi-layer printed circuit board recited in claim 6 is characterized by comprising: a core substrate having through holes; and an interlayer resin insulating layer built up on said core substrate, wherein
said through holes are constituted by filling a first metal layer formed by electroplating, a metal film formed by electroless plating, sputtering or evaporation and a second metal layer formed by electroplating.
Since claim 6 is arranged such that through holes are formed by enclosing plating material, via holes for establishing the connection can be formed on the through holes. Therefore, the wiring density of the via holes can be raised. Since through holes are filled with electroplating, electroless plating and electroplating, insufficient enclosure in each through hole can be prevented. The reliability in the heat-cycle can be improved. Since through holes are filled with electroplating, electroless plating and electroplating, the intensity increases and the warpage does not easily occur.
A method of manufacturing a multi-layer printed circuit board recited in claim 7 comprises at least the following steps (A) to (E):
(A) forming non-penetrating openings in a resin insulating layer incorporating a metal layer formed on either side thereof by applying laser beams such that said non-penetrating openings reach said metal layer;
(B) passing an electric current to each non-penetrating opening formed in said resin insulating layer through said metal layer to fill a first metal layer with electroplating;
(C) forming a metal film on the opposite surface of said resin insulating layer on which said metal layer is formed;
(D) passing an electric current to each non-penetrating opening formed in said resin insulating layer through said metal layer to fill a second metal layer with electroplating; and
(E) etching said metal layer and said metal film of said resin insulating layer to form lands of through holes.
Since claim 7 is arranged such that through holes formed by laser beams, the diameter of each through hole can be reduced to 50 xcexcm to 250 xcexcm. Therefore, the wiring density of the through holes can be raised. Since the through holes are formed by enclosing plating, the strength of the core substrate can be increased. Thus, warpage does not easily occur. Hence it follows that the thickness of the core substrate can be reduced and, therefore, the heat radiation characteristic of the multi-layer printed circuit board can be improved. Since the through holes are filled with electroplating, insufficient filling in each through hole can be prevented. Since a second metal layer is formed in each through hole after metal films serving as lands of the through holes, separation of the lands can be prevented. It leads to a fact that the reliability of the through holes can be improved. Since satisfactory reliability in the connection can be improved, the thickness of each land can be reduced. Therefore, the smoothness and flatness of the interlayer resin insulating layer which is an upper layer can be improved. As a result, separation and formation of a crack in the interlayer resin insulating layer can be prevented.
A method of manufacturing a multi-layer printed circuit board recited in claim 8 further comprises a step for forming a metal layer by electroless plating, sputtering or evaporation according to claim 7.
In claim 8, electroless plating is employed so that the metal layer can be formed with a low cost. When sputtering is employed as a forming method, a metal layer exhibiting excellent adhesiveness and a small thickness can be formed. When an evaporation forming method is employed, a more thin metal layer can be formed.
A method of manufacturing a multi-layer printed circuit board recited in claim 9 is characterized in that said step for forming said metal film on the opposite surface of said resin insulating layer on which said metal layer is formed is arranged to perform electroless plating, sputtering or evaporation, according to claim 7 or 8.
In claim 9, electroless plating is employed so that the metal film can be formed with a low cost. When sputtering is employed as a forming method, a metal layer exhibiting excellent adhesiveness and a small thickness can be formed. When an evaporation forming method is employed, a thin metal layer can be formed.
To solve the above-mentioned problems, a printed circuit board recited in claim 10 is characterized by comprising: a core substrate; and through holes formed in said core substrate, wherein
said core substrate incorporates a core member and a resin insulating layer formed on each of two sides of said core member and having a roughened surface, and
each of said through holes is constituted by providing a metal film for a penetrating opening formed by a laser beam.
In claim 10, laser beams are used to form penetrating in a core substrate constituted by a core member and resin insulating layer formed on each of the two sides of the core member. Since the penetrating openings are, by laser beams, formed in the core substrate which is in a state where the metal film is formed, any retention of an air bubble can be prevented when the metal films are deposited in the penetrating openings to form the through holes. Thus, any corner crack starting with a burr does not occur and, therefore, the reliability in the connection of the through holes can be improved. Since a rough surface is formed on the surface of the core substrate, the adhesiveness with the metal film constituting the through hole can be improved.
In claim 11, the core member is formed by causing the core member to be impregnated with resin. Thus, the strength required for the core substrate can be maintained.
In claim 12, the resin insulating layer is constituted by dispersing soluble particles in refractory resin. Since soluble particles are dissolved, a rough surface can be formed on the surface of the core substrate. Therefore, the adhesiveness of the metal film which is formed on the surface of the core substrate and which constitutes the through hole can be improved.
In claim 13, the resin insulating layer is composed of soluble resin and refractory resin. Since the soluble resin is dissolved, a rough surface can be formed on the surface of the core substrate. Thus, the adhesiveness of the metal film which is formed on the surface of the core substrate can be improved.
According to the invention recited in claim 14, a method of manufacturing a printed circuit board comprises at least the following steps (A) to (D):
(A) laminating a resin insulating layer on each of two sides of a core member to form a core substrate;
(B) forming penetrating openings in said core substrate by applying laser beams;
(C) forming a rough surface on said core substrate; and
(D) providing a metal film for each penetrating opening to form through holes.
In claim 14, penetrating openings are, by laser beams, formed in a core substrate composed of a core member and a resin insulating layer formed on each of the two sides of the core member. Then, a rough surface is formed on the surface of the core substrate, and then a metal film is formed in the penetrating opening. Thus, through holes are formed. The laser beams are used to form the penetrating openings in the core substrate which is in a state before the metal film is formed. Therefore, when the metal film is deposited in each penetrating opening to form the through holes or when the through hole is filled with a filler, retention of any air bubble can be prevented. Thus, any corner crack starting with a burr does not formed and, therefore, reliability in the connection of the through holes can be improved. Since the rough surface is formed on the surface of the core substrate, the adhesiveness with the metal film constituting the through hole can be improved.
In claim 15, the core member is formed by causing the core member to be impregnated with resin. Thus, the strength required for the core substrate can be maintained.
A method of manufacturing a printed circuit board recited in claim 16 comprises said resin insulating layer formed by dispersing soluble particles in refractory resin. Soluble particles are dissolved so that a rough surface is formed on the surface of the core substrate. Thus, the adhesiveness of the metal film which is formed on the surface of the core substrate can be improved.
To solve the above-mentioned problems, a multi-layer printed circuit board resided in claim 17 comprises a core substrate having through holes for connecting the upper and lower surfaces to each other and having a structure that interlayer resin insulating layers and conductor circuits are alternately laminated on said core substrate, wherein
through holes having different diameters are formed in said core substrate.
In an aspect claimed in claim 17, through holes having different diameters are formed in the core substrate. Therefore, the degree of freedom of the wiring density of the through holes can be improved. Since through holes having small diameters serve as power supply lines and ground lines, a multiplicity of power supply lines and ground lines can be provided. Thus, an influence of the inductance of the power supply lines and the ground lines which is exerted on the IC chip can be reduced. As a result, malfunction of the IC chip can prevented.
A multi-layer printed circuit board recited in claim 18 comprises a core substrate having through holes for connecting the upper and lower surfaces to each other and having a structure that interlayer resin insulating layers and conductor circuits are alternately laminated on said core substrate, wherein
through holes each having a small diameter are mainly formed in the central portion of said core substrate, and through holes each having a large diameter are mainly formed in the outer periphery.
A multi-layer printed circuit board recited in claim 19 is characterized by said through holes each having the small diameter are mainly provided with power supply lines and ground lines, and said through holes each having the large diameter are mainly provided with signal lines, according to claim 18.
In claims 18 and 19, through holes each having a small diameter are formed in the central portion of the core substrate and through holes each having a large diameter are formed in the outer periphery. Therefore, the wiring density in the central portion can be raised. Since the through holes formed in the central portion and each having the small diameter serve as the power supply line and the ground lines, a multiplicity of power supply lines and ground lines can be provided. Moreover, the length opening electric wires from the IC chip to an external substrate can be shortened. Therefore, an influence of the inductance of the power supply lines and the ground lines which is exerted on the IC chip can be reduced. As a result, malfunction of the IC chip can be prevented. Note that substitution of expression xe2x80x9cimmediately belowxe2x80x9d for the xe2x80x9ccentral portionxe2x80x9d is permitted.
A method of manufacturing a multi-layer printed circuit board recited in claim 20 comprises at least the following steps (A) and (B);
(A) providing penetrating openings which are formed into through holes and each of which has a small diameter for a core substrate; and
(B) providing penetrating openings which are formed into through holes each having a large diameter for said core substrate.
In claim 20, penetrating openings serving as the through holes and each having a small diameter and penetrating openings each having a large diameter and serving as through holes are formed in the core substrate. Therefore, a core substrate exhibiting a high degree of freedom of the wiring density can be manufactured with a low cost. Each through hole may be formed by either of a laser beam or drilling. It is preferable that the through hole having the small direction is formed by a laser beam. The laser beam may be a carbon dioxide gas laser beam, excimer laser beam, a YAG laser beam or an UV layer. As an alternative to this, an area process using a mask having penetrating opening formed therein or combination of two or more types of laser beams may be employed.
A method of manufacturing a multi-layer printed circuit board recited in claim 21 comprises at least the following steps (A) and (B):
(A) irradiating the central portion of a core substrate with laser beams or drilling the central portion to form penetrating openings which are formed into through holes and each of which has a small diameter; and
(B) irradiating the central portion of said core substrate with laser beams or drilling the central portion to form penetrating openings which are formed into through holes and each of which has a large diameter.
A method of manufacturing a multi-layer printed circuit board recited in claim 22 is characterized by said through holes each having the small diameter are mainly provided with power supply lines and ground lines, and said through holes each having the large diameter are mainly provided with signal lines, according to claim 21.
In aspects claimed in claims 20 and 21, through holes each having a small direction are formed in the central portion of the core substrate by laser beams or by drilling and through holes each having a large diameter are formed in the outer periphery by drilling or a laser beam. Therefore, a core substrate having a high degree of freedom of the wiring density can be formed in the central portion with a low cost. When the through holes each having the small diameter and formed in the central portion serve as the power supply lines and the ground lines, a multiplicity of power supply line and ground lines can be formed. Moreover, the length of each electric wire from the IC chip to the external substrate can be shortened. Therefore, an influence of the inductance of the power supply lines and the ground lines which is exerted on the IC chip can be reduced. As a result, malfunction of the IC chip can be prevented. The through holes each having the large diameter and a low probability of occurrence of a defect in the connection are mainly used as signal lines. Moreover, the through holes each having the small diameter and having a high probability of a defect in the connection are mainly used s the power supply line and the ground lines. Therefore, in a case where the through holes serving as the power supply line and the ground lines encounters disconnection, the multi-layer printed circuit board is able to continue a normal operation.
A printed circuit board and a method of manufacturing said printed circuit board recited in claim 23 comprises a core substrate having the surface on which resin insulating layers and conductor circuits are alternately built up, wherein
said core substrate is constituted by forming openings in a resin plate by applying laser beams and by forming a sputtered layer on said resin plate by sputtering which is performed after said openings have been formed.
A printed circuit board and a method of manufacturing said printed circuit board recited in claim 24 comprises at least the following steps (A) to (F):
(A) forming openings in a resin plate which is formed into a core substrate by applying laser beams;
(B) performing sputtering to form a sputtered layer on said resin plate;
(C) performing electroless plating through said sputtered layer;
(D) forming a resist having a predetermined pattern after said electroless plating has been performed;
(E) performing electroplating to form an electroplated layer in a portion in which said resist is not formed; and
(F) performing etching after said resist has been removed to remove said sputtered layer and said electroless plated layer below said resist so as to form a conductor circuit.
The foregoing process (a) may be performed by using one type of the laser beam or a mixed laser beam of two or more laser beams.
A printed circuit board and a method of manufacturing said printed circuit board recited in claim 25 is characterized by a carbon dioxide laser process, an excimer laser process, a YAG laser process and an UV laser process, when said openings are formed in said resin plate by applying laser beams.
A printed circuit board and a method of manufacturing said printed circuit board recited in claim 26 is characterized in that at least one type of materials selected from Cu, Ni, Cr, Pd and Mo, is employed, when said sputtered layer is formed on said resin plate by sputtering.
A printed circuit board and a method of manufacturing a printed circuit board claimed in claims 23 to 26 have a structure that the resin plate has openings formed by CO2 laser beams (YAG laser beams, excimer laser beams or UV laser beams). Therefore, penetrating openings each having a smaller diameter as compared with that of each of penetrating openings formed by drilling can be formed. As distinct from a structure that openings are formed in a copper-clad laminated board by laser beams, leaving of copper in the through hole which causes a plated film formed in the through hole to be separated can be prevented. Moreover, time required to form the openings can be shortened. The openings are formed in the resin plate by using laser beams, and then one or more elements selected from Cu, Ni, Cr, Pd and Mo is brought into contact with the resin. Therefore, strength between the sputtered layer and the resin of 1.0 kg/cm2 can be realized which is substantially the same as that realized by the conventional copper-clad laminated board.